FACE in ecological research: brief background
FACE is a method and facility used to experimentally enrich the atmosphere enveloping portions of an ecosystem with controlled amounts of carbon dioxide (and other gases in some cases) without using cameras or side walls. Until FACE was implemented in the early 1980s, studies to assess the effects of CO2 enrichment using closed chambers were considered non-representative, as the response of plants and of the whole system were modified to grow in conditions very different from nature. Thus, FACE was developed to study an ecosystem under full exposure to CO2 air controlled concentrations, getting minimal disruption to natural conditions. The results of these experiments provide the best way to estimate how plants and ecosystems respond in a future world where atmospheric CO2 concentrations raise. FACE allows for the investigation of an undisturbed ecosystem without changing its interaction with light, temperature, wind, rainfall, pathogens and insects.
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A typical FACE plot is approximately circular and surrounded by a ring of pipes that release CO2 or CO2-enriched air at vertical intervals, from the edge of the substrate to the top of the plant canopy. In the case of short vegetation, it is enough to have a single vertical release pipe. Wind direction and speed, and the concentration of CO2 are measured at the center of each plot and this information is used by a computer controlled system to adjust the flow rate of CO2 emission in order to maintain the concentration at the target level. To avoid large fluctuations, fast algorithms (the feedback of the immediately previous conditions of the plot) are used. This basic design has been used and verified, with some variations and technical developments, in plots of up to 30 m in diameter, growing vegetation of up to 25 meters.
FACE plots have been used in several parts of the world but have been spatially biased, targeting primarily the temperate ecosystems of northern America and Europe, and more recently Australia. Whereas most FACE faciliies operating in United States and Europe were recently dismantled, others were created in order to study singular or distintive ecosystems in the world. Some representative FACE experiments:
POPFACE (Viterbo, Italy) MiniFACE (various sites in Europe) Tusukuba FACE (Japan) TasFACE (Tasmania Australia) AGFACE (Victoria, Australia) EucFACE (Richmond, Australia) Aspen FACE (Wisconsin, US) SoyFACE (Illinois, US) Duke Forest FACE experiment (North Carolina, US) Nevada Desert FACE Facility (Nevada, US) Oak Ridge National Laboratory (ORNL) FACE (Tennessee, US) |
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In the last decade, some meta-analyses studies about FACE experiments have been publised (e.g. Norby and Zak, 2011; Jones et al., 2014) in order to predict how ecosystems respond to the future. Main conclusions obtained with those FACE experiences were:
References:
Norby RJ, Zak DR (2011) Ecological Lessons from Free-Air CO2 Enrichment (FACE) Experiments. Annual Review of Ecology, Evolution, and Systematics 42: 181-203. Link
Jones AG, Scullion J, Ostle N, Levy PE, Gwynn-Jones D (2014) Completing the FACE of elevated CO2 research. Environment International 73: 252-258. Link
- Net primary productivity is increased by elevated CO2, but the response can diminish over time.
- Carbon accumulation is driven by the distribution of carbon among plant and soil components with differing turnover rates and by interactions between the carbon and nitrogen cycles.
- Plant community structure may change, but elevated CO2 has only minor effects on microbial community structure.
- The locations of these elevated CO2 experiments have been spatially biased, targeting primarily the temperate ecosystems of northern America and Europe. More FACE experiments must be carried out particularly on countries host some of the most important regions for tropical and sub-tropical ecosystems.
- This research lacks understanding of elevated CO2 impacts on tropical forests and boreal regions, which are potentially the most significant biomes for C sink and storage activity, respectively.
- A global validation on NPP is needed, especially in the most important biomes for C processing.
- Few research programs have addressed elevated CO2 effects on below-ground C storage, such that at the global scale, no overall responses are discernable.
References:
Norby RJ, Zak DR (2011) Ecological Lessons from Free-Air CO2 Enrichment (FACE) Experiments. Annual Review of Ecology, Evolution, and Systematics 42: 181-203. Link
Jones AG, Scullion J, Ostle N, Levy PE, Gwynn-Jones D (2014) Completing the FACE of elevated CO2 research. Environment International 73: 252-258. Link